Re: oom_killer crash linux system

[Minchan Kim]

On Tue, Oct 19, 2010 at 11:59 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> On Tue, 19 Oct 2010 10:07:38 +0800
> "Figo.zhang" <zhangtianfei@xxxxxxxxxxxxxxxx> wrote:
>
>>
>> >
>> > very lots of change ;)
>> > can you please send us your crash log?
>>
>> i add some prink in select_bad_process() and oom_badness() to see
>> pid/totalpages/points/memoryuseage/and finally process to selet to kill.
>>
>> i found it the oom-killer select: syslog-ng,mysqld,nautilus,VirtualBox
>> to kill, so my question is:
>>
>> 1. the syslog-ng,mysqld,nautilus is the system foundamental process, so
>> if oom-killer kill those process, the system will be damaged, such as
>> lose some important data.
>>
>> 2. the new oom-killer just use percentage of used memory as score to
>> select the candidate to kill, but how to know this process to very
>> important for system?
>>
>
> The kernel can never know it. Just an admin (a man or management software) knows.
> Old kernel tries to guess it, but it tend to be wrong and many many report comes
> "why my ....is killed..." All guesswork the kernel does is not enough, I think.
>
>> oom_score_adj, it is anyone commercial linux distributions to use this
>> to protect the critical process.
>>
> oom_adj may be used in some system. All my customers select panic_at_oom=1
> and cause cluster fail over rather than half-broken.
>
> <Off topic>
> Your another choice is memory cgroup, I think.
> please see documentation/cgroup/memory.txt or libcgroup.
> http://sourceforge.net/projects/libcg/
> You can use some fancy controls with it.
> </Off topic>
>
>
> BTW, there seems to be some strange things.
> (CC'ed to linux-mm)
> Brief Summary:
>   an oom-killer happens on swapless environment with 2.6.36-rc8.
>   It has 2G memory.
> a reporter says
> ==
>> i want to test the oom-killer. My desktop (Dell optiplex 780, i686
>> kernel)have 2GB ram, i turn off the swap partition, and open a huge pdf
>> files and applications, and let the system eat huge ram.
>>
>> in 2.6.35, i can use ram up to 1.75GB,
>>
>> but in 2.6.36-rc8, i just use to 1.53GB ram , the system come very slow
>> and crashed after some minutes , the DiskIO is very busy. i see the
>> DiskIO read is up to 8MB/s, write just only 400KB/s, (see by conky).
> ==
>
> The trigger of oom-kill is order=0 allocation. (see original mail for full log)
>
>
> Oct 19 09:44:08 myhost kernel: [  618.441470] httpd invoked oom-killer:
> gfp_mask=0x201da, order=0, oom_adj=0, oom_score_adj=0
>
> Zone's stat is.
>
> Oct 19 09:44:08 myhost kernel: [  618.441551]
> DMA free:7968kB min:64kB low:80kB high:96kB active_anon:3700kB inactive_anon:3752kB
>    active_file:12kB inactive_file:252kB unevictable:0kB isolated(anon):0kB
>    isolated(file):0kB present:15788kB mlocked:0kB dirty:0kB writeback:4kB
>    mapped:52kB shmem:348kB slab_reclaimable:0kB slab_unreclaimable:16kB
>    kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB
>    writeback_tmp:0kB pages_scanned:421 all_unreclaimable? yes
>    lowmem_reserve[]: 0 865 1980 1980
>
> Oct 19 09:44:08 myhost kernel: [  618.441560]
> Normal free:39348kB min:3728kB low:4660kB high:5592kB active_anon:176740kB
>       inactive_anon:25640kB active_file:84kB inactive_file:308kB
>       unevictable:0kB isolated(anon):0kB isolated(file):0kB present:885944kB
>       mlocked:0kB dirty:0kB writeback:4kB mapped:576992kB shmem:5024kB
>       slab_reclaimable:7612kB slab_unreclaimable:15512kB kernel_stack:2792kB
>       pagetables:6884kB unstable:0kB bounce:0kB writeback_tmp:0kB
>       pages_scanned:741 all_unreclaimable? yes
>       lowmem_reserve[]: 0 0 8921 8921
>
> Oct 19 09:44:08 myhost kernel: [  618.441569]
> HighMem free:392kB min:512kB low:1712kB high:2912kB active_anon:492208kB
>        inactive_anon:166404kB active_file:180kB inactive_file:840kB
>        unevictable:40kB isolated(anon):0kB isolated(file):0kB present:1141984kB
>        mlocked:40kB dirty:0kB writeback:12kB mapped:493648kB shmem:72216kB
>        slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB
>        pagetables:0kB unstable:0kB bounce:0kB writeback_tmp:0kB
>        pages_scanned:1552 all_unreclaimable? yes
>
> Highmem seems a bit strange.
>  present(1141984) - active_anon - inactive_anon - inactive_file - active_file
>  = 482352kB but free is 392kB.
>
>  Highmem is used for some other purpose than usual user's page.(pagetable is 0.)
>  And, Hmm, mapped:493648kB seems too large for me.
>  (active/inactive-file + shmem is not enough.)
>  And "mapped" in NORMAL zone is large, too.
>
>  Does anyone have idea about file-mapped-but-not-on-LRU pages ?

Isn't it possible some file pages are much sharable?
Please see the page_add_file_rmap.

>
> Thanks,
> -Kame
>
>
>
>
>
>
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-- 
Kind regards,
Minchan Kim
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